[PATCH v7 0/5] Add DAX ABI for memmap_on_memory

[Vishal Verma]

This series adds sysfs ABI to control memmap_on_memory behavior for DAX
devices.

Patch 1 replaces incorrect device_lock() usage with a local rwsem - this
was identified during review.

Patch 2 is also a preparatory patch that replaces sprintf() for sysfs
operations with sysfs_emit()

Patch 3 adds the missing documentation for the sysfs ABI for DAX regions
and Dax devices.

Patch 4 exports mhp_supports_memmap_on_memory().

Patch 5 adds the new ABI for toggling memmap_on_memory semantics for dax
devices.

---
Changes in v7:
- Rebase to v6.8-rc1
- Remove an unnecessary 'size' variable. (Matthew)
- Replace device lock (ab)use in dax/bus.c with local rwsems (Greg)
- Replace sprintf() usage with sysfs_emit() (Greg)
- Link to v6: https://lore.kernel.org/r/20231214-vv-dax_abi-v6-0-ad900d698438@xxxxxxxxx

Changes in v6:
- Use sysfs_emit() in memmap_on_memory_show() (Greg)
- Change the ABI documentation date for memmap_on_memory to January 2024
  as that's likely when the 6.8 merge window will fall (Greg)
- Fix dev->driver check (Ying)
- Link to v5: https://lore.kernel.org/r/20231214-vv-dax_abi-v5-0-3f7b006960b4@xxxxxxxxx

Changes in v5:
- Export and check mhp_supports_memmap_on_memory() in the DAX sysfs ABI
  (David)
- Obtain dax_drv under the device lock (Ying)
- Check dax_drv for NULL before dereferencing it (Ying)
- Clean up some repetition in sysfs-bus-dax documentation entries
  (Jonathan)
- A few additional cleanups enabled by guard(device) (Jonathan)
- Drop the DEFINE_GUARD() part of patch 2, add dependency on Dan's patch
  above so it can be backported / applied separately (Jonathan, Dan)
- Link to v4: https://lore.kernel.org/r/20231212-vv-dax_abi-v4-0-1351758f0c92@xxxxxxxxx

Changes in v4:
- Hold the device lock when checking if the dax_dev is bound to kmem
  (Ying, Dan)
- Remove dax region checks (and locks) as they were unnecessary.
- Introduce guard(device) for device lock/unlock (Dan)
- Convert the rest of drivers/dax/bus.c to guard(device)
- Link to v3: https://lore.kernel.org/r/20231211-vv-dax_abi-v3-0-acf6cc1bde9f@xxxxxxxxx

Changes in v3:
- Fix typo in ABI docs (Zhijian Li)
- Add kernel config and module parameter dependencies to the ABI docs
  entry (David Hildenbrand)
- Ensure kmem isn't active when setting the sysfs attribute (Ying
  Huang)
- Simplify returning from memmap_on_memory_store()
- Link to v2: https://lore.kernel.org/r/20231206-vv-dax_abi-v2-0-f4f4f2336d08@xxxxxxxxx

Changes in v2:
- Fix CC lists, patch 1/2 didn't get sent correctly in v1
- Link to v1: https://lore.kernel.org/r/20231206-vv-dax_abi-v1-0-474eb88e201c@xxxxxxxxx

Cc: <linux-kernel@xxxxxxxxxxxxxxx>
Cc: <nvdimm@xxxxxxxxxxxxxxx>
Cc: <linux-cxl@xxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: <linux-mm@xxxxxxxxx>
To: Dan Williams <dan.j.williams@xxxxxxxxx>
To: Vishal Verma <vishal.l.verma@xxxxxxxxx>
To: Dave Jiang <dave.jiang@xxxxxxxxx>
To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
To: Oscar Salvador <osalvador@xxxxxxx>

---
Vishal Verma (5):
      dax/bus.c: replace driver-core lock usage by a local rwsem
      dax/bus.c: replace several sprintf() with sysfs_emit()
      Documentatiion/ABI: Add ABI documentation for sys-bus-dax
      mm/memory_hotplug: export mhp_supports_memmap_on_memory()
      dax: add a sysfs knob to control memmap_on_memory behavior

 include/linux/memory_hotplug.h          |   6 +
 drivers/dax/bus.c                       | 295 +++++++++++++++++++++++---------
 mm/memory_hotplug.c                     |  17 +-
 Documentation/ABI/testing/sysfs-bus-dax | 153 +++++++++++++++++
 4 files changed, 381 insertions(+), 90 deletions(-)
---
base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
change-id: 20231025-vv-dax_abi-17a219c46076

Best regards,
-- 
Vishal Verma <vishal.l.verma@xxxxxxxxx>